I think VOM and current metering are covered really well in the Protective Relaying book by blackburn. The power calculation handbook also has a few problems.
As an aside I thought using the two volt meters for three phase power question in the NCEES sample exam was really awesome.
I think NEC has ground resistance ranges to deduce whether you should add another electrode to the system, it varies if it's residential or commercial. In terms of good books on measuring, I'm say the power engineers handbook by beatty or the westinghouse transmission and distribution book (american electrician's handbook). I know they are hard to read but conceptually having one of these books during the exam would be worth their weight in gold.
You can probably get the specifications for insulation tests simply by going to like megger and looking up their manuals or articles. UL even is a good source, since they have the test ratings for the low and high voltage sides of switchgear.
